Overall objectives of this proposed investigation are: (1) to develop efficient and highly stereochemically controlled methods for the synthesis of steroid side chains of physiologically important steroids including insect molting hormones, vitamin D3 and its metabolites, cholesterol, bile acids and some plant hormones. This will undoubtedly contribute to the methodological advancement in the synthesis of chiral acyclic compounds; (2) to obtain pertinent information on the mechanism of important biological reactions of natural products, especially, the stereochemical aspects of biological oxidation. We would like to propose the following specific aims with the general objectives mentioned above: (a) Development of the stereochemically controlled synthetic methods of 22-hydroxy- and 20,22-dihydroxy-side chains of steroids present in insect molting hormones and the biosynthetic intermediates leading to androgens from cholesterol. (b) Stereocontrolled synthesis of plant hormones, oogoniol and brassinolide. (c) Elucidation of the molecular mechanism of hte steroid side chain cleavage by the mammalian adrenal cortex enzyme system that yields pregnenolone. (d) Stereochemical studies of the mechanism of the enzymatic oxidation of a steroidal methyl group using chirally labelled 19-methyl steroids and microsomal fractions of placenta. (e) Synthesis of the optically active presqualene alcohol which is a biosynthetic precursor to all steroidal hormones and triterpenes and the unambiguous assignment of its absolute configuration.